Evolution of large-scale circulation and heating during the first transition of Asian summer monsoon

This study investigates the characteristics of large-scale circulation and heating during the first transition of the Asian summer monsoon by a compositing technique. The first transition is characterized by a sudden change in large-scale atmospheric circulation and convective activity in South and Southeast Asia. The most notable features include 1) the development of the low-level cyclonic circulation and the upper-level anticyclone in South Asia, 2) the strong convection in the Bay of Bengal, the Indochina peninsula, and the South China Sea, and 3) the warming and the subsequent cooling of the SST in the Bay of Bengal. Results show the close relationship between the fluctuations of atmospheric circulation, heating, and surface condition. It is suggested that the atmospheric circulation abruptly changes during the transition owing to the interaction between convection, large-scale circulation, and lower-boundary forcing that includes topographically lifting ocean and land surface heating.